EP1087912B1 - Device and method for centrifuging mineral fibers - Google Patents

Description

The invention relates to the manufacture of mineral fibers of the fiber type glass of fine diameter, in particular at most 3 µm, in order to incorporate them in papers used more particularly for making aerosol filters or battery separators.

It is in fact known from patents EP-B-0 267 092 and EP-B-0 430 770 from paper sheets for such applications containing fibers. It's about generally a mixture of two types of fibers: "fine" fibers of a average diameter of the order of 2 to 3 µm at least and "very fine" fibers with a diameter of less than 1 µm. The former are more particularly intended to mechanically reinforce the paper, to give it the "bulk" necessary, while the seconds create the porosity giving it its filtration properties. As proposed in the two aforementioned patents, these two types of fiber can advantageously be obtained by a process known as of internal centrifugation, widely used elsewhere to manufacture fibers used to make thermal or sound insulation products. Schematically, this process consists in introducing a stream of molten glass in a centrifuge, also called fiberizing plate, rotating at high speed speed and pierced at its periphery by a very large number of orifices per which the glass is projected in the form of filaments under the effect of force centrifugal. These filaments are then subjected to the action of an annular current. drawing at high temperature and speed along the wall of the centrifuge, stream that thins them and turns them into fibers. The fibers formed are entrained by this gaseous stretching stream towards a receiving device generally consisting of a gas permeable strip. This known process has is the subject of numerous improvements including those taught in patents EP-B-0 189 354 or EP-B-0 519 797.

For thermal or sound insulation, the fibers manufactured by such process generally have a diameter greater than 3 µm, generally from about 4 to 4.5 µm up to 12 µm: we cannot therefore use the process in its conventional operating parameters to get the fibers "fine" or "very fine" mentioned above. Some adaptations are therefore necessary to obtain fine fibers by this process. Thus the patent EP-B-0 267 092 cited above offers in particular a specific selection of speed drawing gases to obtain them.

The object of the invention is therefore to improve the device and the method fiber drawing by internal centrifugation of fine mineral fibers with a diameter of plus 3 µm, improvement targeting in particular the quality of the fibers obtained and / or their production yield.

The invention firstly relates to a centrifuge device internal of mineral fibers of diameter less than or equal to 3 µm, comprising a centrifuge fitted with a peripheral band pierced with orifices and which has a fiber drawing height less than or equal to 35 mm, preferably less than or equal to 32.5 or 30 mm, for example between 16 and 32.5 mm.

In the context of the invention, the "drawing height" of the centrifuge by the distance from the highest point of the belt peripheral of the lowest "holes" thereof, "high" and "low" comprising with reference to the centrifuge arranged in the centrifugation position, that is to say along a substantially vertical axis (of rotation).

Conventionally, fibers of standard diameter are manufactured for isolation using wide peripheral band centrifuges, having, for give an order of magnitude, a drawing height of at least 40 mm. We have indeed advantage to choose a large fiber height, since it allows to increase the number of orifices in the peripheral band, to have a high number of rows of orifices leading to increasing the capacity of production, often expressed as "pull" equal to the number of kg of fibers of glass produced daily and by centrifuge. This reasoning of course has limits, because production capacity is also linked to many other parameters and should not be obtained at the price of too significant a quantity infibers, grains, risks of malfunction of the centrifuge, etc ... So you also have to take into account, for example, the gradients of temperature which can settle on the height of the peripheral band or whether or not high temperature drawing gases have the same impact on all rows of orifices.

It turned out that the quality could be considerably increased so-called "fine" fibers, less than 3 µm in diameter, by selecting a particular fiber height, below 35 to 30 mm or less, i.e. at values much lower than those used conventionally and those used until now to make so-called "fine" fibers of less than 3 .mu.m. With such a type of centrifuge, of lower height, we have seen that the "fine" fibers produced were much more stable dimensionally, with a very reduced quantity of type defects fiber / grain or amalgam fiber stuck together, and they had very satisfactory mechanical properties, particularly in terms of value yield strength.

In addition, the implementation of the centrifuge was simpler, less delicate than that encountered until now in the production of fibers "fine". This increase in quality and this greater feasibility were not obtained at the cost of a reduction in the economically unbearable production capacity, on the one hand because "fine" fibers with a very specific application have a high added value and that we can also afford a little lower production capacity to that obtained for standard fibers, and on the other hand because it could be possible to at least partially limit the drop in production capacity by adapting, in particular by increasing, the drilling density of the strip peripheral.

Advantageously, the centrifuge according to the invention is chosen to average diameter less than or equal to 800 mm, in particular at least 200 mm, for example around 200, 400, or 600 mm.

To obtain "fine" fibers no more than 3 µm in diameter, it is preferable that the holes in the centrifuge be of a diameter of at most 1.5 mm, for example at most 1.2 mm, in particular between 1.1 and 0.5 mm, for example between 0.9 and 0.7 mm (here we refer to a "diameter", because these orifices are generally all chosen circular, it is not excluded however that the orifices are not circular, in this case it is necessary understand "diameter" by "larger dimension").

According to the invention, the orifices of the strip centrifuge device are grouped in rows arranged in concentric circles over the height of the strip. In the invention, at least two adjacent rows have holes of different diameters. It is advantageous, that the rows have, from the top to the bottom of the peripheral band, hole diameters decreasing (generally all the orifices in the same row have the same diameter). We can thus provide, from top to bottom, n row (s) of orifices of a given diameter, then p row (s) of holes of smaller diameter, then t row (s) of further reduced diameter orifices, etc ... with: n, p and t ≥ 1.

By establishing a sort of decreasing "gradient" in size orifices from top to bottom, there has been an improvement in the quality fiberizing. We were thus able to reduce the differences in the way filaments from the highest rows were fiberized compared to those lowest rows: this "gradient" allows development of primary filaments at the outlet of orifices and a stretching limiting the crossings of trajectory, and therefore shocks, between the fibers being drawn from rows of different orifices hence the gain in quality observed.

Preferably, the orifices of the centrifuge are grouped in rows spaced from each other by a distance between 1 and 2 mm, in particular between 1.2 and 1.8 mm, preferably with an offset pitch of one row to row between 1 and 2 mm, especially between 1.8 and 1.3 mm and a spacing between two orifices in the same row of between 2.2 and 1.4 mm, especially between 2.1 and 1.6 mm.

Advantageously, the device according to the invention comprises means high temperature gas drawing in the form of an annular burner. he has thus proved particularly useful in controlling the production of "fine" fibers to provide a means for channeling these drawing gases at high temperature and / or the mineral matter ejected from the centrifuge transforming of fiber filaments, medium in the form of a gas blowing ring not hot, at room temperature for example. We can also plan optionally a means of external heating of the walls of the centrifuge, especially in its lowest part, in the form of an annular inductor. All these elements are notably described in their principle of operation in the aforementioned patents EP-B-0 189 354 and EP-B-0 519 797.

Can also be used an "internal" heating means at centrifuge, of the internal burner type. This can fulfill different roles, in particular to complete the thermal conditioning of the molten glass in the "basket" of the centrifuge (term explained below using the figures), maintain the glass reserve in the centrifuge at an appropriate temperature, finally to continuously re-melt the fibers likely to have stuck on the outer walls of the centrifuge.

The "external" heating means of the annular inductor type can be advantageously combined with this internal heating means, it allows also to better control the temperature of the glass reserve and the recasting of the bonded fibers. It has in fact been found that, generally, for weak draws it was enough to simply use a burner internal, whereas for high pulls, the annular inductor was found necessary, the internal burner optionally complementing it advantageously.

The invention also relates to a process for the formation of fibers. "fine" minerals with a diameter of 3 µm or less by centrifugation internal associated with a high temperature gas drawing, in particular implement the device described above. This process involves dumping the material to be fiberized in a centrifuge with a peripheral band pierced orifices, with a drawing height (defined above) of the centrifuge less than or equal to 35 mm, in particular at most 32.5 mm and advantageously between 16 and 32.5 mm.

The centrifuge is advantageously the one whose characteristics have described above.

on peut de préférence régler la température des gaz en sortie de brûleur à au moins 1350°C, notamment au moins 1400°C et par exemple entre 1400 et 1500°C, notamment entre 1430 et 1470°C. On adapte ensuite la température en fonction du type de composition minérale à fibres, suivant notamment son comportement viscosimétrique. Ces valeurs de température se sont révélées les plus favorables pour produire des fibres " fines ",

avantageusement, on règle aussi la vitesse des gaz émis par le brûleur à au moins 200 m/s, mesurée juste à la sortie des lèvres du brûleur) notamment à des valeurs comprises entre 200 et 295 m/s,

enfin, on règle de préférence la largeur annulaire des gaz en sortie de brûleur à des valeurs comprises entre 5 mm et 9 mm.

The hot gas drawing is advantageously carried out by an annular burner, the operating parameters of which can be chosen as follows:

the temperature of the gases leaving the burner can preferably be adjusted to at least 1350 ° C., in particular at least 1400 ° C. and for example between 1400 and 1500 ° C., in particular between 1430 and 1470 ° C. The temperature is then adapted according to the type of mineral composition with fibers, in particular according to its viscosimetric behavior. These temperature values have proven to be the most favorable for producing "fine" fibers,

advantageously, the speed of the gases emitted by the burner is also adjusted to at least 200 m / s, measured just at the outlet of the lips of the burner) in particular to values between 200 and 295 m / s,

finally, the annular width of the gases leaving the burner is preferably adjusted to values between 5 mm and 9 mm.

When the process of the invention uses a means for channeling the hot drawing gases and / or the material ejected from the orifices of the centrifuge under the effect of centrifugal force, it is advantageously a ring of blowing the gas which is at most at room temperature, and under a supply gas pressure of between 0.5 and 2.5 × 10 ⁵ Pa, in particular 0.7 to 2.10 ⁻⁵ Pa.

In fact, in the context of the invention, the use of a crown blowing has proven particularly advantageous: its "cold" air jets (usually at room temperature) have a cooling effect beneficial to the fibers being stretched, and that all particularly when it comes to "fine" fibers which are of interest to the invention. This cooling in fact avoids "over-stretching" of the fibers and turbulence which tends to shorten them, to weaken them. It therefore contributes to guarantee good mechanical properties to the fibers, which is all the more important that here the fiberizing zone is reduced in height compared to a fiberizing of standard dimensions fibers: there is thus a clear distinction, and advantageous, between on the one hand the stretching zone subjected to the influence of ring burner and the cooling zone subject to the influence of annular blower (the latter remains optional, however).

An inductor can be used to heat the lowest area of the centrifuge and avoid or limit the creation of a temperature gradient on the height of the centrifuge. However as here the centrifuge has a height relatively weak, it is only optional. As mentioned above, we can also, cumulatively or alternatively, use an internal burner.

The method according to the invention makes it possible to alternate capacities of production fully compatible with economic imperatives, given the quality of the fiber obtained (generally less than 1.5 to 2% by weight of grains / fiber). We were thus able to obtain draws of diameter between 2 and 3 µm, for example 2.6 µm, of the order of 0.5 kg per day per centrifuge orifice, which corresponds to pulls industrial of the order of 2500 to 7700 kg per day and per centrifuge for centrifuges with an average diameter of 400 mm and a drawing height between 16 and 32.5 mm.

The subject of the invention is also the use of the fibers obtained by the device and / or process described above, with a maximum diameter of 3 µm, in the manufacture of paper in particular with a view to producing filters or battery separators.

A subject of the invention is also paper, incorporating these fibers. "fines" with a diameter of at most 3 µm (generally between 2 and 3 µm) and "very fine" mineral fibers with a diameter of at most 1 µm (generally between 0.2 and 0.8 µm). If the invention relates rather to "fine" fibers, it is not excluded that it also relates to the manufacture of "very fine" fibers.

Advantageously, the mass proportion between the two types of fibers is between 25/75 and 75/25, especially around 60/40 to 40/60.

• figure 1 : une vue partielle du dispositif de centrifugation selon l'invention,
• figure 2 : une vue partielle en coupe du centrifugeur selon la figure 1.

The invention will be detailed below with the aid of nonlimiting examples illustrated by the following figures:

• FIG. 1 : a partial view of the centrifuge device according to the invention,
• FIG. 2 : a partial sectional view of the centrifuge according to FIG. 1.

FIG. 1 therefore represents a partial view of a system of internal centrifuge with hot gas drawing adapted from those known from the prior art and described in particular, in patents EP-91,866, EP-189,354 and EP-519,797, to which reference may be made for more details on the generality of this fiberizing mode.

The system comprises a centrifuge 1 fixed on a shaft 2. The shaft and the centrifuge are rotated rapidly by means of a motor not shown. The shaft 2 is hollow and the glass in the molten state flows from the supply means not shown in the shaft 2 up to "basket" 3 in which the molten glass is spread. Basket 3 is also rotated so that the molten glass is projected onto the wall peripheral 4 which is pierced with orifices and, from there, in the form of nets bulky 6 on the peripheral wall 7 of the centrifuge 1, which will form on this wall a permanent reserve of molten glass supplying the circular holes 14 drilled in said wall. This wall 7 is inclined about 5 to 10 ° from the vertical. Many holes circulars 14 arranged in rows, emerge from the flow cones 8 extending in front-fibers 15, projected into the annular gas stream emitted by the burner 9. Under the action of this current, these pre-fibers stretch, their terminal portion generating discontinuous fibers 10 then collected under the centrifuge. The system also includes a blowing ring 11 which creates a "gas layer" surrounding the annular gas stream generated by the burner 9. Optionally, a crown is also used induction 12 under the centrifuge 1 and / or an internal burner not shown.

Under standard operating conditions, such a device provides fibers with an average diameter of at least 4 µm, in particular on the order of 5 to 12 µm.

un diamètre moyen d'au plus 3 µm, notamment entre 2,3 et 3 µm, par exemple centré sur 2,6 ou 2,8 ou 3 µm,

avec un faible taux de défauts (grains, infibrés, fibres recollées), notamment d'au plus 2% en poids de fibres fabriquées,

avec des propriétés mécaniques suffisamment élevées pour qu'elles puissent renforcer des papiers dans des applications de filtres ou de séparateurs de batteries, dont notamment une résistance à la traction d'au moins 1,3 lb/inch, soit au moins environ 228 N/m, mesurée selon une méthode standardisée sur un équipement de mesure spécifique à l'industrie papetière.

avec une tirée satisfaisante pour ce type de fibres, notamment d'au moins 0,5 kg de fibres par jour et par orifice de centrifugeur.

The invention therefore consisted in obtaining fibers meeting the following criteria:

an average diameter of at most 3 μm, in particular between 2.3 and 3 μm, for example centered on 2.6 or 2.8 or 3 μm,

with a low defect rate (grains, infibers, glued fibers), in particular at most 2% by weight of manufactured fibers,

with sufficiently high mechanical properties that they can reinforce papers in filter or battery separator applications, including in particular a tensile strength of at least 1.3 lb / inch, or at least about 228 N / m, measured using a standardized method on measuring equipment specific to the paper industry.

with a satisfactory draft for this type of fiber, in particular at least 0.5 kg of fiber per day and per orifice of the centrifuge.

Two types of glass compositions were tested, type "1" and type "2". Table 1 below indicates for each of them the weight percentages of their constituents and the value of their temperature T _log3 in ° C. which is the temperature of the compositions when their viscosity is equal, in poise, to log 3 (the Fe ₂ O _{3 level} corresponds to the total iron level of the composition expressed in this oxidized form).

The most significant adaptation made in the context of the invention for achieve the objectives according to the invention concerned the dimensions of the base centrifugation, the sectional view of which has been enlarged in FIG. 2.

The plates chosen have a diameter D of 400 mm.

la hauteur de la première rangée d'orifices H₁, mesurée entre le point P₁ le plus haut de la bande périphérique et le niveau P2 de la première rangée,

la hauteur de perçage H₂, correspondant à la distance séparant la première rangée P2 de la dernière rangée P3,

la hauteur de fibrage H₃, correspondant à la distance entre le point P₁ le plus haut de la bande périphérique et la dernière rangée P3,

la hauteur totale H₄, correspondant à la distance entre le point le plus haut P1 et le point le plus bas P4 de la bande périphérique.

Their peripheral band is characterized by different dimensions, and more particularly:

the height of the first row of orifices H ₁ , measured between the highest point P ₁ of the peripheral strip and the level P2 of the first row,

the drilling height H ₂ , corresponding to the distance separating the first row P2 from the last row P3,

the fiber drawing height H ₃ , corresponding to the distance between the highest point P ₁ of the peripheral strip and the last row P3,

the total height H ₄ , corresponding to the distance between the highest point P1 and the lowest point P4 of the peripheral strip.

l'épaisseur e de l'assiette,

le nombre d'orifices total N,

le pas de décalage des orifices d'une rangée à l'autre,

le nombre d'orifices n par rangée,

le nombre de rangées r

la répartition des diamètres d'orifices selon les rangées.

Other parameters are also characteristic, in particular:

the thickness e of the plate,

the total number of orifices N,

the no offset of the orifices from one row to another,

the number of orifices n per row,

the number of rows r

the distribution of hole diameters according to the rows.

As regards the dimensions of the peripheral strip, the most characteristic is H ₃ the fiber height. Here, it is reduced to values between, for example, 16 and 32.5 mm.

Table 2 below groups together examples of ranges of values for H ₁ , H ₂ , H ₃ , H ₄ , expressed in mm: H ₁ 6 - 10 H ₂ 10 - 25.5 H ₃ 16 - 32.5 H ₄ 20 - 36.5

The number of rows r can vary for example from 7 to 22 rows, in particular 9 to 20 rows, with in particular from 600 to 770 orifices per row,

The total number of orifices N per plate can thus be from 5,000 to 16,940 holes.

Advantageously, it is expected that the diameter of the orifices is between 0.9 and 0.7 mm, with a distribution of diameter per row such that the diameter of the orifices decreases from top to bottom. Thus, we can have 3 rows of orifices at 0.9 mm, then 3 rows of orifices at 0.8 mm then 3 rows of orifices of 0.7 mm from top to bottom, i.e. n ₁ rows of diameter d ₁ , n ₂ rows of diameter d ₂ , n _i rows of diameter d _i , etc ... with generally n ₁ , n ₂ , n _i , ... at least equal to 2, and d _i > d _{i + 1} .

Such a decreasing gradient in the size of the orifices contributes to obtaining higher quality fibers.

In addition to the choice of the size of the centrifuges, the invention also relates to adaptations of certain parameters of operation.

Thus, it is preferable to choose a high gas temperature at the outlet of the annular burner 9, which however is adjusted as a function of the hardness of the glass which we want to fiberize, evaluated for example by its temperature T _log3 : the temperature of the gases is chosen here around 1430 ° C to 1470 ° C for glass types 1 and 2.

We also found that the combination of the gradient in the drilling of holes in the centrifuge with a particular configuration of the centrifuge made it possible to obtain fibers with improved mechanical properties. This configuration consists, in particular, in adjusting the height of the basket in the centrifuge so that the basket feeds rather the part superior of the "reserve".

In conclusion, the modifications made to the centrifugation process internal have produced high quality and feasible fine fibers economically and industrially.

Claims (17)

1. Apparatus for internally centrifuging fine mineral fibres with a diameter less than or equal to 3 µm, comprising a centrifuge (1) equipped with a peripheral belt in which holes have been drilled, characterised in that the height (H₃) to which said centrifuge (1) draws out the fibres - defined by the distance that separates the uppermost point of said peripheral belt from the lowermost holes in said belt when the centrifuge is viewed in its centrifuging position - is less than or equal to 35 mm, and that the holes (14) of the centrifuge (1) are arranged in rows disposed in concentric circles over the height of the peripheral belt, with at least two adjacent rows presenting different hole diameters.
2. Apparatus according to claim 1, characterised in that the fibre-drawing height (H₃) is less than or equal to 32.5 mm.
3. Apparatus according to claim 2, characterised in that the fibre-drawing height (H₃) is between 16 and 32.5 mm.
4. Apparatus according to any of the preceding claims, characterised in that the diameter of the holes (14) decreases with each row, from the top to the bottom of the peripheral belt of the centrifuge in the centrifuging position.
5. Apparatus according to any of the preceding claims, characterised in that the centrifuge (1) has a mean diameter (D) less than or equal to 800 mm, more particularly not less than 200 mm.
6. Apparatus according to any of the preceding claims, characterised in that the diameter (d) of at least some of the holes of the centrifuge (1) is not more than 1.5 or 1.2 mm, more particularly between 1.1 and 0.5 mm, for example between 0.9 and 0.7 mm.
7. Apparatus according to any of the preceding claims, characterised in that the rows of holes are spaced apart from one another by a distance of between 1 and 2 mm, more particularly between 1.2 and 1.8 mm, preferably with an interval of between 1 and 2 mm from one row to the next, for example between 1.3 and 1.8 mm, and a spacing of between 2.2 and 1.4 mm, for example between 2.1 and 1.6 mm, between two holes in any one row.
8. Apparatus according to any of the preceding claims, characterised in that it includes at least one high-temperature gas drawing means in the form of an annular burner (9).
9. Apparatus according to claim 8, characterised in that it includes at least one means for conducting the high-temperature drawing gases and/or the mineral material ejected from the centrifuge (1), in the form of a blowing ring (11) for gas at the ambient temperature.
10. Apparatus according to any of the preceding claims, characterised in that it includes an external heating means for the walls of the centrifuge, more particularly the lowermost part of the centrifuge (1) in the centrifuging position, in the form of an inductor (12) and/or an internal heating means of the internal burner type.
11. Method for forming fine mineral fibres with a diameter less than or equal to 3 µm, by internal centrifugation thereof in association with a high-temperature gas drawing process, where the material that is being made into fibres is poured into a centrifuge (1) the peripheral belt of which is drilled with holes (14), characterised in that the height (H₃) to which said centrifuge (1) draws out the fibres - defined by the distance that separates the uppermost point of said peripheral belt from the lowermost holes in said belt when the centrifuge is viewed in its centrifuging position - is less than or equal to 35 mm, and that the holes (14) of the centrifuge (1) are arranged in rows disposed in concentric circles over the height of the peripheral belt, with at least two adjacent rows presenting different hole diameters.
12. Method according to claim 11, characterised in that the high-temperature gas drawing process is carried out by an annular burner (9), with a gas exit temperature from the burner of not less than 1350°C, more particularly not less than 1400°C, and preferably between 1400 and 1500°C.
13. Method according to claim 12, characterised in that the annular burner (9) generates drawing gases with a velocity of at least 200 m/s, more particularly between 200 and 295 m/s, and preferably with an annular width of between 5 and 9 mm at the burner exit.
14. Method according to any of claims 11 to 13, characterised in that said method utilises a means for conducting the high-temperature drawing gases and/or the material for fibre-making which has been ejected from the centrifuge, in the form of a blowing ring (11) for gas at no higher than the ambient temperature, the gas feed pressure of which is more particularly between 0.5.10^-5 and 2.10⁵ Pa.
15. Method according to any of claims 11 to 14, characterised in that said method utilises an external heating means of the inductor type (12) to heat the lowermost zone of the centrifuge and/or an internal heating means of the internal burner type.
16. Use of the mineral fibres with a diameter of not more than 3 µm obtained using the apparatus according to any of claims 1 to 10 and/or by the method according to any of claims 11 to 15, for manufacturing papers, more particularly with a view to producing filters and battery dividers.
17. A paper incorporating mineral fibres with a diameter of not more than 3 µm, more particularly between 2 and 3 µm, obtained with the apparatus according to any of claims 1 to 10 and/or by the method according to any of claims 11 to 15, and mineral fibres with a diameter of not more than 1 µm, more particularly between 0.2 and 0.8 µm.

Images